As is well known, liquid crystal molecules are essentially linear in structure so that such molecules can be said to have a major axis. Also, the molecules, in general, are asymmetric so that it is relevant to speak of the molecules as having a preferred or specific orientation. Thus, a pair of molecules may not only be parallel or transverse to each other but may also be anti-parallel to each other. For example, rotation of an asymmetric linear molecule through an angle of 180.degree. places the molecule in a position in which it is anti-parallel to its original position.
Where a liquid crystal display device is to operate in the twisted nematic mode, the relationship between the plane of polarization of polarized light falling on the molecules and the direction of the major axis of the molecules becomes pertinent. Specifically, transmission of light through the device is greater for light vibrating perpendicularly to the major axis direction of the liquid crystal molecules than for light vibrating in parallel with said major axis. Even when only a single liquid crystal layer is interposed between polarizer and analyzer plates, significant variations in contrast and visibility as the result of variation in the angle between the plane of polarization of incident light and orientation of the liquid crystal molecules in the nearer portion of the liquid crystal layer have been found. Where the number of liquid crystal layers is greater than one, namely when a poly-layer device is used, the loss of contrast and visibility as the result of random choice of the angle between plane polarized light entering each layer and the orientation of the molecules at the nearer surface of the layer can be severe. Accordingly, a construction in which orientation directions are such as to maximize visibility and contrast present substantial advantages. The construction of a single-layer liquid crystal cell which operates in the twisted nematic mode and which has a preferred viewing direction is described in U.S. Pat. No. 3,941,454, said patent being incorporated herein by reference as though presented in full.